Method and apparatus for transmitting channel state information-reference signals in wireless communication system

ABSTRACT

A method of transmitting channel state information (CSI)-reference signals (RS) at a base station in a wireless communication system includes generating a reference signal sequence, and mapping the reference signal sequence to resource elements (REs) included in one or more patterns for 8-port CSI-RS transmission among five patterns for 8-port CSI-RS transmission located in a first region of a PRB pair and three patterns for 8-port CSI-RS transmission located in a second region of the PRB pair. A maximum of two OFDM (orthogonal frequency division multiplexing) symbols is used for a physical downlink control channel in a subframe including the PRB pair.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2013/008209, filed on Sep. 11, 2013,which claims the benefit of U.S. Provisional Application Ser. No.61/699,789, filed on Sep. 11, 2012, the contents of which are all herebyincorporated by reference herein in their entirety.

TECHNICAL FIELD

The following description relates to a wireless communication systemand, more particularly, to a method and apparatus for transmittingchannel state information (CSI)-reference signals (RSs).

BACKGROUND ART

Wireless communication systems have been widely deployed in order toprovide various types of communication services including voice or data.In general, a wireless communication system is a multiple access systemthat can support communication with multiple users by sharing availablesystem resources (a bandwidth, transmission power, etc.). Examples ofmultiple access systems include Code Division Multiple Access (CDMA),Frequency Division Multiple Access (FDMA), Time Division Multiple Access(TDMA), Orthogonal Frequency Division Multiple Access (OFDMA), SingleCarrier Frequency Division Multiple Access (SC-FDMA), Multi CarrierFrequency Division Multiple Access (MC-FDMA), etc.

DISCLOSURE Technical Problem

An object of the present invention devised to solve the problem lies ina technologies related to transmission of more than 8 channel stateinformation (CSI)-reference signals (RSs).

It will be appreciated by persons skilled in the art that the objectsthat could be achieved with the present invention are not limited towhat has been particularly described hereinabove and the above and otherobjects that the present invention could achieve will be more clearlyunderstood from the following detailed description.

Technical Solution

The object of the present invention can be achieved by providing amethod of transmitting channel state information (CSI)-reference signals(RSs) at a base station in a wireless communication system, includinggenerating a reference signal sequence, and mapping the reference signalsequence to resource elements (REs) included in one or more patterns for8-port CSI-RS transmission among five patterns for 8-port CSI-RStransmission located in a first region of a PRB pair and three patternsfor 8-port CSI-RS transmission located in a second region of the PRBpair, wherein a maximum of two OFDM symbols is used for a physicaldownlink control channel in a subframe including the PRB pair.

In another aspect of the present invention, provided herein is a basestation apparatus for transmitting channel state information(CSI)-reference signals (RSs) in a wireless communication system,including a transmission module and a processor, wherein the processorgenerates a reference signal sequence, and maps the reference signalsequence to resource elements (REs) included in one or more patterns for8-port CSI-RS transmission among five patterns for 8-port CSI-RStransmission located in a first region of a PRB pair and three patternsfor 8-port CSI-RS transmission located in a second region of the PRBpair, and wherein a maximum of two OFDM symbols is used for a physicaldownlink control channel in a subframe including the PRB pair.

The aspects of the present invention include some or all of thefollowing features.

The three patterns for 8-port CSI-RS transmission located in the secondregion of the PRB pair may be used only for 64-port CSI-RS transmission.

The three patterns for 8-port CSI-RS transmission located in the secondregion may be prohibited from being set as zero-power CSI-RSs.

If the reference signal sequence is for 64-port CSI-RSs, both the fivepatterns for 8-port CSI-RSs transmission located in the first region andthe three patterns for 8-port CSI-RSs transmission located in the secondregion may be used.

If the reference signal sequence is for 32-port CSI-RSs, all the fivepatterns for 8-port CSI-RSs transmission located in the first region maybe used.

The first region may be included in last two orthogonal frequencydivision multiplexing (OFDM) symbols of a first slot of the PRB pair andthird and fourth OFDM symbols and last two OFDM symbols of a second slotof the PRB pair, and the second region may be included in third andfourth OFDM symbols of the first slot of the PRB pair.

The patterns for 8-port CSI-RS transmission may include a first RE, anRE having an index which is one less than an index of the first RE in afrequency axis direction, an RE having an index which is one greaterthan an index of the first RE in a time axis direction and an RE havingan index which is one less in the frequency axis direction than an indexof the RE having the index which is one greater than an index of thefirst RE in the time axis direction and a second RE, an RE having anindex which is one less than an index of the second RE in the frequencyaxis direction, an RE having an index which is one greater than an indexof the second RE in the time axis direction and an RE having an indexwhich is one less in the frequency axis direction than an index of theRE having the index which is one greater than an index of the second REin the time axis direction, in the PRB pair.

The second RE may be located to be separated from the first RE by 6subcarriers on a frequency axis.

The first RE included in the first region may be located at (11, 2), (9,2), (7, 2) and (9, 5) at each slot of the PRB pair and (integer 1,integer 2)=(subcarrier index, OFDM symbol index).

The first RE included in the first region may be located at (11, 2), (9,2) and (7, 2) at a first slot of the PRB pair and (integer 1, integer2)=(subcarrier index, OFDM symbol index).

The reference signal sequence may be for one of 16-port, 32-port or64-port CSI-RSs.

Information about the subframe may be transmitted to a user equipment inadvance.

Advantageous Effects

According to the present invention, it is possible to supporttransmission of more than 8 channel state information (CSI)-referencesignals (RSs).

It will be appreciated by persons skilled in the art that the effectsthat can be achieved with the present invention are not limited to whathas been particularly described hereinabove and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

In the drawings:

FIG. 1 illustrates the structure of a radio frame;

FIG. 2 illustrates the structure of a downlink resource grid for theduration of one downlink slot;

FIG. 3 illustrates the structure of a downlink subframe;

FIG. 4 illustrates the structure of an uplink subframe;

FIG. 5 is a view referred to for describing Reference Signals (RSs);

FIG. 6 is a diagram illustrating a channel state information(CSI)-reference signal (RS);

FIGS. 7 to 10 are diagrams illustrating embodiments of the presentinvention; and

FIG. 11 is a diagram showing the configuration of atransmission/reception apparatus.

BEST MODE

The embodiments of the present invention described hereinbelow arecombinations of elements and features of the present invention. Theelements or features may be considered selective unless otherwisementioned. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent invention may be constructed by combining parts of the elementsand/or features. Operation orders described in embodiments of thepresent invention may be rearranged. Some constructions or features ofany one embodiment may be included in another embodiment and may bereplaced with corresponding constructions or features of anotherembodiment.

In the embodiments of the present invention, a description is made,centering on a data transmission and reception relationship between aBase Station (BS) and a User Equipment (UE). The BS is a terminal nodeof a network, which communicates directly with a UE. In some cases, aspecific operation described as performed by the BS may be performed byan upper node of the BS.

Namely, it is apparent that, in a network comprised of a plurality ofnetwork nodes including a BS, various operations performed forcommunication with a UE may be performed by the BS or network nodesother than the BS. The term ‘BS’ may be replaced with the term ‘fixedstation’, ‘Node B’, ‘evolved Node B (eNode B or eNB)’, ‘Access Point(AP)’, etc. The term ‘relay’ may be replaced with the term ‘Relay Node(RN)’ or ‘Relay Station (RS)’. The term ‘terminal’ may be replaced withthe term ‘UE’, ‘Mobile Station (MS)’, ‘Mobile Subscriber Station (MSS)’,‘Subscriber Station (SS)’, etc.

Specific terms used for the embodiments of the present invention areprovided to help the understanding of the present invention. Thesespecific terms may be replaced with other terms within the scope andspirit of the present invention.

In some cases, to prevent the concept of the present invention frombeing ambiguous, structures and apparatuses of the known art will beomitted, or will be shown in the form of a block diagram based on mainfunctions of each structure and apparatus. Also, wherever possible, thesame reference numbers will be used throughout the drawings and thespecification to refer to the same or like parts.

The embodiments of the present invention can be supported by standarddocuments disclosed for at least one of wireless access systems,Institute of Electrical and Electronics Engineers (IEEE) 802, 3^(rd)Generation Partnership Project (3GPP), 3GPP Long Term Evolution (3GPPLTE), LTE-Advanced (LTE-A), and 3GPP2. Steps or parts that are notdescribed to clarify the technical features of the present invention canbe supported by those documents. Further, all terms as set forth hereincan be explained by the standard documents.

Techniques described herein can be used in various wireless accesssystems such as Code Division Multiple Access (CDMA), Frequency DivisionMultiple Access (FDMA), Time Division Multiple Access (TDMA), OrthogonalFrequency Division Multiple Access (OFDMA), Single Carrier-FrequencyDivision Multiple Access (SC-FDMA), etc. CDMA may be implemented as aradio technology such as Universal Terrestrial Radio Access (UTRA) orCDMA2000. TDMA may be implemented as a radio technology such as GlobalSystem for Mobile communications (GSM)/General Packet Radio Service(GPRS)/Enhanced Data Rates for GSM Evolution (EDGE). OFDMA may beimplemented as a radio technology such as IEEE 802.11 (Wi-Fi), IEEE802.16 (WiMAX), IEEE 802.20, Evolved-UTRA (E-UTRA) etc. UTRA is a partof Universal Mobile Telecommunications System (UMTS). 3GPP LTE is a partof Evolved UMTS (E-UMTS) using E-UTRA. 3GPP LTE employs OFDMA fordownlink and SC-FDMA for uplink. LTE-A is an evolution of 3GPP LTE.WiMAX can be described by the IEEE 802.16e standard (WirelessMetropolitan Area Network (WirelessMAN)-OFDMA Reference System) and theIEEE 802.16m standard (WirelessMAN-OFDMA Advanced System). For clarity,this application focuses on the 3GPP LTE and LTE-A systems. However, thetechnical features of the present invention are not limited thereto.

With reference to FIG. 1, the structure of a radio frame will bedescribed below.

In a cellular Orthogonal Frequency Division Multiplexing (OFDM) wirelesspacket communication system, uplink and/or downlink data packets aretransmitted in subframes. One subframe is defined as a predeterminedtime period including a plurality of OFDM symbols. The 3GPP LTE standardsupports a type-1 radio frame structure applicable to Frequency DivisionDuplex (FDD) and a type-2 radio frame structure applicable to TimeDivision Duplex (TDD).

FIG. 1(a) illustrates the type-1 radio frame structure. A downlink radioframe is divided into 10 subframes. Each subframe is further dividedinto two slots in the time domain. A unit time during which one subframeis transmitted is defined as a Transmission Time Interval (TTI). Forexample, one subframe may be 1 ms in duration and one slot may be 0.5 msin duration. A slot includes a plurality of OFDM symbols in the timedomain and a plurality of Resource Blocks (RBs) in the frequency domain.Because the 3GPP LTE system adopts OFDMA for downlink, an OFDM symbolrepresents one symbol period. An OFDM symbol may be referred to as anSC-FDMA symbol or symbol period. An RB is a resource allocation unitincluding a plurality of contiguous subcarriers in a slot.

The number of OFDM symbols in one slot may vary depending on a CyclicPrefix (CP) configuration. There are two types of CPs: extended CP andnormal CP. In the case of the normal CP, one slot includes 7 OFDMsymbols. In the case of the extended CP, the length of one OFDM symbolis increased and thus the number of OFDM symbols in a slot is smallerthan in the case of the normal CP. Thus when the extended CP is used,for example, 6 OFDM symbols may be included in one slot. If channelstate gets poor, for example, during fast movement of a UE, the extendedCP may be used to further decrease Inter-Symbol Interference (ISI).

In the case of the normal CP, one subframe includes 14 OFDM symbolsbecause one slot includes 7 OFDM symbols. The first two or three OFDMsymbols of each subframe may be allocated to a Physical Downlink ControlCHannel (PDCCH) and the other OFDM symbols may be allocated to aPhysical Downlink Shared Channel (PDSCH).

FIG. 1(b) illustrates the type-2 radio frame structure. A type-2 radioframe includes two half frames, each having 5 subframes, a DownlinkPilot Time Slot

(DwPTS), a Guard Period (GP), and an Uplink Pilot Time Slot (UpPTS).Each subframe is divided into two slots. The DwPTS is used for initialcell search, synchronization, or channel estimation at a UE. The UpPTSis used for channel estimation and acquisition of uplink transmissionsynchronization to a UE at an eNB. The GP is a period between an uplinkand a downlink, which eliminates uplink interference caused by multipathdelay of a downlink signal. One subframe includes two slots irrespectiveof the type of a radio frame.

The above-described radio frame structures are purely exemplary and thusit is to be noted that the number of subframes in a radio frame, thenumber of slots in a subframe, or the number of symbols in a slot mayvary.

FIG. 2 illustrates the structure of a downlink resource grid for theduration of one downlink slot. A downlink slot includes 7 OFDM symbolsin the time domain and an RB includes 12 subcarriers in the frequencydomain, which does not limit the scope and spirit of the presentinvention. For example, a downlink slot may include 7 OFDM symbols inthe case of the normal CP, whereas a downlink slot may include 6 OFDMsymbols in the case of the extended CP. Each element of the resourcegrid is referred to as a Resource Element (RE). An RB includes 12×7 REs.The number of RBs in a downlink slot, N^(DL) depends on a downlinktransmission bandwidth. An uplink slot may have the same structure as adownlink slot.

FIG. 3 illustrates the structure of a downlink subframe. Up to threeOFDM symbols at the start of the first slot in a downlink subframe areused for a control region to which control channels are allocated andthe other OFDM symbols of the downlink subframe are used for a dataregion to which a PDSCH is allocated. Downlink control channels used inthe 3GPP LTE system include a Physical Control Format Indicator CHannel(PCFICH), a Physical Downlink Control CHannel (PDCCH), and a PhysicalHybrid automatic repeat request (HARQ) Indicator CHannel (PHICH). ThePCFICH is located in the first OFDM symbol of a subframe, carryinginformation about the number of OFDM symbols used for transmission ofcontrol channels in the subframe. The PHICH delivers an HARQACKnowledgment/Negative ACKnowledgment (ACK/NACK) signal in response toan uplink transmission. Control information carried on the PDCCH iscalled Downlink Control Information (DCI). The DCI transports uplink ordownlink scheduling information, or uplink transmission power controlcommands for UE groups. The PDCCH delivers information about resourceallocation and a transport format for a Downlink Shared CHannel(DL-SCH), resource allocation information about an Uplink Shared CHannel(UL-SCH), paging information of a Paging CHannel (PCH), systeminformation on the DL-SCH, information about resource allocation for ahigher-layer control message such as a Random Access Responsetransmitted on the PDSCH, a set of transmission power control commandsfor individual UEs of a UE group, transmission power controlinformation, Voice Over Internet Protocol (VoIP) activation information,etc. A plurality of PDCCHs may be transmitted in the control region. AUE may monitor a plurality of PDCCHs. A PDCCH is formed by aggregatingone or more consecutive Control Channel Elements (CCEs). A CCE is alogical allocation unit used to provide a PDCCH at a coding rate basedon the state of a radio channel. A CCE includes a plurality of REgroups. The format of a PDCCH and the number of available bits for thePDCCH are determined according to the correlation between the number ofCCEs and a coding rate provided by the CCEs. An eNB determines the PDCCHformat according to DCI transmitted to a UE and adds a Cyclic RedundancyCheck (CRC) to control information. The CRC is masked by an Identifier(ID) known as a Radio Network Temporary Identifier (RNTI) according tothe owner or usage of the PDCCH. If the PDCCH is directed to a specificUE, its CRC may be masked by a cell-RNTI (C-RNTI) of the UE. If thePDCCH is for a paging message, the CRC of the PDCCH may be masked by aPaging Indicator Identifier (P-RNTI). If the PDCCH carries systeminformation, particularly, a System Information Block (SIB), its CRC maybe masked by a system information ID and a System Information RNTI(SI-RNTI). To indicate that the PDCCH carries a Random Access Responsein response to a Random Access Preamble transmitted by a UE, its CRC maybe masked by a Random Access-RNTI (RA-RNTI).

FIG. 4 illustrates the structure of an uplink subframe. An uplinksubframe may be divided into a control region and a data region in thefrequency domain. A Physical Uplink Control CHannel (PUCCH) carryinguplink control information is allocated to the control region and aPhysical Uplink Shared Channel (PUSCH) carrying user data is allocatedto the data region. To maintain the property of a single carrier, a UEdoes not transmit a PUSCH and a PUCCH simultaneously. A PUCCH for a UEis allocated to an RB pair in a subframe. The RBs of the RB pair occupydifferent subcarriers in two slots. Thus it is said that the RB pairallocated to the PUCCH is frequency-hopped over a slot boundary.

Reference Signals (RSs)

In a wireless communication system, a packet is transmitted on a radiochannel. In view of the nature of the radio channel, the packet may bedistorted during the transmission. To receive the signal successfully, areceiver should compensate for the distortion of the received signalusing channel information. Generally, to enable the receiver to acquirethe channel information, a transmitter transmits a signal known to boththe transmitter and the receiver and the receiver acquires knowledge ofchannel information based on the distortion of the signal received onthe radio channel. This signal is called a pilot signal or an RS.

In the case of data transmission and reception through multipleantennas, knowledge of channel states between Transmission (Tx) antennasand Reception (Rx) antennas is required for successful signal reception.Accordingly, an RS should be transmitted through each Tx antenna.

RSs may be divided into downlink RSs and uplink RSs. In the current LTEsystem, the uplink RSs include:

i) DeModulation-Reference Signal (DM-RS) used for channel estimation forcoherent demodulation of information delivered on a PUSCH and a PUCCH;and

ii) Sounding Reference Signal (SRS) used for an eNB or a network tomeasure the quality of an uplink channel in a different frequency.

The downlink RSs are categorized into:

i) Cell-specific Reference Signal (CRS) shared among all UEs of a cell;

ii) UE-specific RS dedicated to a specific UE;

iii) DM-RS used for coherent demodulation of a PDSCH, when the PDSCH istransmitted;

iv) Channel State Information-Reference Signal (CSI-RS) carrying CSI,when downlink DM-RSs are transmitted;

v) Multimedia Broadcast Single Frequency Network (MBSFN) RS used forcoherent demodulation of a signal transmitted in MBSFN mode; and

vi) positioning RS used to estimate geographical position informationabout a UE.

RSs may also be divided into two types according to their purposes: RSfor channel information acquisition and RS for data demodulation. Sinceits purpose lies in that a UE acquires downlink channel information, theformer should be transmitted in a broad band and received even by a UEthat does not receive downlink data in a specific subframe. This RS isalso used in a situation like handover. The latter is an RS that an eNBtransmits along with downlink data in specific resources. A UE candemodulate the data by measuring a channel using the RS. This RS shouldbe transmitted in a data transmission area.

CRSs serve two purposes, that is, channel information acquisition anddata demodulation. A UE-specific RS is used only for data demodulation.CRSs are transmitted in every subframe in a broad band and CRSs for upto four antenna ports are transmitted according to the number of Txantennas in an eNB.

For example, if the eNB has two Tx antennas, CRSs for antenna ports 0and 1 are transmitted. In the case of four Tx antennas, CRSs for antennaports 0 to 3 are respectively transmitted.

FIG. 5 illustrates patterns in which CRSs and DRSs are mapped to adownlink RB pair, as defined in a legacy 3GPP LTE system (e.g.conforming to Release-8). An RS mapping unit, i.e. a downlink RB pairmay include one subframe in time by 12 subcarriers in frequency. Thatis, an RB pair includes 14 OFDM symbols in time in the case of thenormal CP (see FIG. 5(a)) and 12 OFDM symbols in time in the case of theextended CP (see FIG. 5(b)).

In FIG. 5, the positions of RSs in an RB pair for a system where an eNBsupports four Tx antennas are illustrated. Reference numerals 0, 1, 2and 3 denote the REs of CRSs for first to fourth antenna ports, antennaport 0 to antenna port 3, respectively, and reference character ‘D’denotes the positions of DRSs.

CSI-RS

CSI-RS is an RS used for channel measurement in an LTE-A systemsupporting up to eight antenna ports on downlink. CSI-RS differs in thisaspect from CRS used for both channel measurement and data demodulationand thus it is not necessary to transmit CSI-RSs in every subframe likeCRSs. CSI-RS is used in Transmission Mode 9 . For data demodulation,DM-RS is used.

More specifically, CSI-RSs may be transmitted through 1, 2, 4 or 8antenna ports. Antenna 15 may be used for one antenna port, antennaports 15 and 16 for two antenna ports, antenna ports 15 to 18 for fourantenna ports, and antenna ports 15 to 22 for eight antenna ports.

CSI-RSs may be generated by the following [Equation 1].

$\begin{matrix}{{{r_{l,n_{s}}(m)} = {{\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {2\; m} \right)}}} \right)} + {j\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {{2\; m} + 1} \right)}}} \right)}}},\mspace{79mu}{m = 0},1,\ldots\mspace{14mu},{N_{RB}^{\max,{DL}} - 1}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$Where r_(l,n) _(s) (m) denotes the generated CSI-RSs, c(i) denotes apseudo-random sequence, n_(s) is a slot number, l is an OFDM symbolindex, and N_(RB) ^(max, DL) denotes the maximum number of RBs in adownlink bandwidth.

The CSI-RSs generated by [Equation 1] may be mapped to REs on aper-antenna port basis by the following equation.

$\begin{matrix}{\mspace{79mu}{{a_{k,l}^{(p)} = {w_{l^{n}} \cdot {r_{l,n_{s}}\left( m^{\prime} \right)}}}{k = {k^{\prime} + {12\; m} + \left\{ {{\begin{matrix}{- 0} & {{{{for}\mspace{14mu} p} \in \left\{ {15,16} \right)},{{normal}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}} \\{- 6} & {{{{for}\mspace{14mu} p} \in \left\{ {17,18} \right)},{{normal}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}} \\{- 1} & {{{{for}\mspace{14mu} p} \in \left\{ {19,20} \right)},{{normal}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}} \\{- 7} & {{{{for}\mspace{14mu} p} \in \left\{ {21,22} \right)},{{normal}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}} \\{- 0} & {{{{for}\mspace{14mu} p} \in \left\{ {15,16} \right)},{{extended}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}} \\{- 3} & {{{{for}\mspace{14mu} p} \in \left\{ {17,18} \right)},{{extended}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}} \\{- 6} & {{{{for}\mspace{14mu} p} \in \left\{ {19,20} \right)},{{extended}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}} \\{- 9} & {{{{for}\mspace{14mu} p} \in \left\{ {21,22} \right)},{{extended}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}}\end{matrix}l} = {l^{\prime} + \left\{ {{\begin{matrix}l^{''} & \begin{matrix}{{C\; S\; I\mspace{14mu}{reference}\mspace{11mu}{signal}\mspace{14mu}{configurations}\mspace{14mu} 0\text{-}19},} \\{{normal}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}\end{matrix} \\{2\; l^{''}} & \begin{matrix}{{C\; S\; I\mspace{14mu}{reference}\mspace{11mu}{signal}\mspace{14mu}{configurations}\mspace{14mu} 20\text{-}31},} \\{{normal}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}\end{matrix} \\l^{''} & \begin{matrix}{{C\; S\; I\mspace{14mu}{reference}\mspace{11mu}{signal}\mspace{14mu}{configurations}\mspace{14mu} 0\text{-}27},} \\{{extended}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}\end{matrix}\end{matrix}\mspace{79mu} w_{l^{''}}} = \left\{ {{{\begin{matrix}1 & {p \in \left\{ {15,17,19,21} \right\}} \\\left( {- 1} \right)^{''} & {p \in \left\{ {16,18,20,22} \right\}}\end{matrix}\mspace{79mu} l^{''}} = 0},{{1\mspace{79mu} m} = 0},1,\ldots\mspace{14mu},{{N_{RB}^{DL} - {1\mspace{79mu} m^{\prime}}} = {m + \left\lfloor \frac{N_{RB}^{\max,{DL}} - N_{RB}^{DL}}{2} \right\rfloor}}} \right.} \right.}} \right.}}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

In [Equation 2], k′ and l′ may be determined according to CSI-RSconfigurations as illustrated in [Table 1].

TABLE 1 CSI RS Number of CSI RSs configured Con- 1 or 2 4 8 figu- n_(s)n_(s) n_(s) ration (k′, l′) mod 2 (k′, l′) mod 2 (k′, l′) mod 2 Frame 0(9, 5) 0 (9, 5) 0 (9, 5) 0 struc- 1 (11, 2)  1 (11, 2)  1 (11, 2)  1ture 2 (9, 2) 1 (9, 2) 1 (9, 2) 1 type 3 (7, 2) 1 (7, 2) 1 (7, 2) 1 1and 4 (9, 5) 1 (9, 5) 1 (9, 5) 1 2 5 (8, 5) 0 (8, 5) 0 6 (10, 2)  1 (10,2)  1 7 (8, 2) 1 (8, 2) 1 8 (6, 2) 1 (6, 2) 1 9 (8, 5) 1 (8, 5) 1 10 (3,5) 0 11 (2, 5) 0 12 (5, 2) 1 13 (4, 2) 1 14 (3, 2) 1 15 (2, 2) 1 16 (1,2) 1 17 (0, 2) 1 18 (3, 5) 1 19 (2, 5) 1 Frame 20 (11, 1)  1 (11, 1)  1(11, 1)  1 struc- 21 (9, 1) 1 (9, 1) 1 (9, 1) 1 ture 22 (7, 1) 1 (7, 1)1 (7, 1) 1 type 23 (10, 1)  1 (10, 1)  1 2 only 24 (8, 1) 1 (8, 1) 1 25(6, 1) 1 (6, 1) 1 26 (5, 1) 1 27 (4, 1) 1 28 (3, 1) 1 29 (2, 1) 1 30(1, 1) 1 31 (0, 1) 1

By Equation 2 and Table 1, CSI-RSs are mapped to REs as shown in FIG. 6.In FIG. 6, numeral denotes a CSI-RS port and an actual port number maybe obtained by adding 15 to this numeral. More specifically, referringto FIG. 6, a reference signal for one CSI-RS port is spread over twoconsecutive OFDM symbols and two CSI-RSs share two REs distinguishedusing an orthogonal sequence. For example, REs denoted by numerals 0 and1 mean two REs in which CSI-RS ports 0 and 1 are transmitted.

In FIG. 6, if the number of CSI-RSs is 2, that is, in case of 2-portCSI-RS, the REs used for CSI-RS transmission are two REs, which areconsecutive in a time axis direction, among equally hatched REs. In caseof 4-port CSI-RS, REs used for CSI-RS transmission are REs correspondingto four consecutive numerals from equally hatched 0^(th) and 4^(th) REs.In case of 8-port CSI-RS, a reference signal sequence is mapped toequally hatched REs.

As described above, the CSI-RSs may not be transmitted in every subframebut may be transmitted in a specific subframe. More specifically, theCSI-RSs may be transmitted in a subframe satisfying Equation 3 below byreferring to a CSI-RS subframe configuration shown in Table 2.

TABLE 2 CSI-RS CSI-RS subframe periodicity T_(CSI-RS) offset Δ_(CSI-RS)CSI-RS-SubframeConfig I_(CSI-RS) (subframes) (subframes) 0-4 5I_(CSI-RS)  5-14 10 I_(CSI-RS) - 5 15-34 20 I_(CSI-RS) - 15 35-74 40I_(CSI-RS) - 35  75-154 80 I_(CSI-RS) - 75(10n _(f) +└n _(s)/2┘−Δ_(CSI-RS))modT_(CSI-RS)=0  [Equation 3]where T_(CSI-RS) denotes the transmission period of CSI-RSs, Δ_(CSI-RS)is an offset, n_(f) is a system frame number, and n_(s) is a slotnumber.

These CSI-RSs may be signaled to a UE in a CSI-RS config InformationElement (IE) described in [Table 3] below.

TABLE 3 CSI-RS-Config-r10::= SEQUENCE { csi-RS-r10 CHOICE { releaseNULL, setup SEQUENCE { antennaPortsCount-r10 ENUMERATED {an1, an2, an4,an8}, resourceConfig-r10 INTEGER (0..31), subframeConfig-r10 INTEGER(0..154), p-C-r10 INTEGER (−8.. 15) } } OPTIONAL, -- Need ONzeroTxPowerCSI-RS-r10 CHOICE { release NULL, setup SEQUENCE {zeroTxPowerResourceConfigList-r10 BIT STRING (SIZE (16)),zeroTxPowerSubframeConfig-r10 INTEGER (0..154) } } OPTIONAL -- Need ON }

In [Table 3], ‘antennaPortsCount-r10’ indicates the number of antennasthrough which CSI-RSs are transmitted (one of 1, 2, 4 and 8 isselected), and ‘resourceConfig-r10’ specifies REs carrying the CSI-RSsin one RB in the time-frequency domain. ‘subframeConfig-r10’ indicates asubframe carrying the CSI-RSs and the ratio of a CSI-RS Energy PerResource Element (EPRE) to a PDSCH EPRE. In addition, the eNB transmitsinformation about zero-power CSI-RSs.

In the CSI-RS Config IE, ‘resourceConfig-r10’ indicates the positions ofthe CSI-RSs. Specifically, ‘resourceConfig-r10’ indicates the positionsof symbols and subcarriers carrying the CSI-RSs in one RB according to aCSI-RS configuration number ranging from 0 to 31 in [Table 1].

As described above, currently, in the LTE-A system, only 8-port CSI-RStransmission is supported. In consideration of 3D MIMO, massive MIMO,etc., 16-port, 32-port or 64-port CSI-RS transmission needs to besupported. Accordingly, a CSI-RS transmission structure will now bedescribed.

Embodiment 1

Embodiment 1 relates to a method of transmitting CSI-RSs of more than 8ports using REs for CSI-RSs defined in existing LTE-A system andadditional REs in a single subframe. Hereinafter, for convenience ofdescription, a region including REs for CSI-RSs in existing LTE-A systemis referred to as a first region and a region including REs newlydefined in order to transmit CSI-RSs of more than 8 ports is referred toas a second region. As shown in FIG. 6, the first region includes 5patterns for 8-port CSI-RS transmission and the second region includesthree patterns for 8-port CSI-RS transmission. That is, CSI-RStransmission of more than 8 ports may use one or more patterns amongfive patterns for 8-port CSI-RS transmission of the first region andthree patterns for 8-port CSI-RS transmission of the second region.

The position of the second region is shown in FIG. 7, for example. InFIG. 7, the same numeral denotes REs configuring one 8-port CSI-RS. Inother words, numeral x denotes an 8-port CSI-RS pattern x. In FIG. 7,8-port CSI-RS patterns 0, 1, 2, 3 and 4 are REs defined in existingLTE-A system and correspond to the first region and 8-port CSI-RSpatterns 5, 6 and 7 correspond to the second region. That is, in theexample of FIG. 7, the second region is included in third and fourthOFDM symbols of a first slot. The present invention is not limited tothe example of FIG. 7 and the second region may be included in OFDMsymbols other than OFDM symbols in which the first region is included.

As shown in FIG. 7, if the second region, that is, the three patternsfor additional 8-port CSI-RS transmission, is defined, 16-, 32-, 64-portCSI-RS transmission may be performed as follows. All 64-port CSI-RSs maybe transmitted in one subframe using all 8 patterns, that is, 8-portCSI-RS patterns 0 to 7. 32-port CSI-RSs may be transmitted using 8-portCSI-RS patterns 1, 2, 3 and 4 or 8-port CSI-RS patterns 5, 6, 7 and 0.16-port CSI-RSs may be transmitted using 8-port CSI-RS patterns 1 and 2,8-port CSI-RS patterns 3 and 4, 8-port CSI-RS patterns 5 and 6 or 8-portCSI-RS patterns 7 and 0. For such CSI-RS transmission, a PDCCH may betransmitted only using a maximum of two OFDM symbols. Accordingly,information about the subframe using only a maximum of two OFDM symbols(disregarding a PCFICH) may be transmitted to the UE in advance.Alternatively, the eNB may inform the UE that the 8-port CSI-RS patternsof the second region is used and the UE which receives this informationmay determine that the PDCCH is transmitted only in a maximum of twoOFDM symbols in the corresponding subframe.

As another example, three patterns for 8-port CSI-RS transmissionlocated in the second region may be defined to be used only for 64-portCSI-RS transmission. In this case, 64-port CSI-RSs may be transmittedusing all 8 patterns, that is, 8-port CSI-RS patterns 0 to 7. 32-portCSI-RSs may be transmitted using 8-port CSI-RS patterns 1, 2, 3 and 4.16-port CSI-RSs may be transmitted using 8-port CSI-RS patterns 1 and 2or 8-port CSI-RS patterns 3 and 4. In addition, 8-port CSI-RS patterns5, 6 and 7 of the second region may be prohibited from being set aszero-power CSI-RSs. Preferably, CSI is fed back to a UE located at acell center using all 64-port CSI-RSs and is fed back to a UE located ata cell edge using CSI-RSs of less than 64 ports in terms of feedbackoverhead and performance improvement. Since interference of aneighboring cell is not large with respect to the UE located at the cellcenter, a possibility that 8-port CSI-RS patterns 5, 6 and 7 are set aszero-power CSI-RSs does not need to be applied to peripheraltransmission points.

The positions of the three patterns for 8-port CSI-RS transmissionlocated in the second region shown in FIG. 7 will now be described.First, REs corresponding to patterns for 8-port CSI-RS transmissioninclude a first RE 701, an RE 702 having an index which is one less thanan index of the first RE in a frequency axis direction, an RE 703 havingan index which is one greater than an index of the first RE in a timeaxis direction, an RE 704 having an index which is one less in thefrequency axis direction than an index of the RE 703 having the indexwhich is one greater than an index of the first RE in the time axisdirection, a second RE 711, an RE 712 having an index which is one lessthan an index of the second RE in the frequency axis direction, an RE713 having an index which is one greater than an index of the second REin the time axis direction, an RE 714 having an index which is one lessin the frequency axis direction than an index of the RE 713 having theindex which is one greater than an index of the second RE in the timeaxis direction. The second RE may be separated from the first RE by 6subcarriers on the frequency axis. In this case, the first RE includedin the second region is located at (11, 2), (9, 2) and (7, 2) in a firstslot of the PRB pair. Here, (integer 1, integer 2)=(subcarrier index,OFDM symbol index). Similarly, the first RE included in the first regionis located at (11, 2), (9, 2), (7, 2) and (9, 5) in each slot of the PRBpair.

FIG. 8 shows embodiments of an MBSFN subframe supporting PDSCHtransmission in the normal CP case. FIG. 8(a) shows the case that thesecond region is located at fourth and fifth OFDM symbols of the firstslot, FIG. 8(b) shows the case that the second region is located atfirst and second OFDM symbols of the second slot and FIG. 8(c) shows thecase that the second region is located at third and fourth OFDM symbolsof the first slot. In FIG. 8, descriptions except for the position ofthe second region and the PDCCH, refer to FIG. 7.

Embodiment 2

Embodiment 2 relates to a method of transmitting N-port CSI-RSs usingonly patterns for 8-port CSI-RSs included in the first region. In thiscase, since additional REs defined for CSI-RSs are not present, onlyCSI-RS transmission on a maximum of 32 ports is possible. FIG. 9 showsfive patterns (8-port CSI-RS patterns 0 to 4) for 8-port CSI-RStransmission of the first region.

If 16-port CSI-RSs are transmitted according to Embodiment 2, two of thefive patterns for 8-port CSI-RS transmission may be selected. Ingeneral, in case of 8*M, in order to specify REs used for 8*M-portCSI-RS transmission, M existing 8-port CSI-RS patterns located in thesame subframe are specified. That is, for 8*M-port CSI-RS transmission,the UE is informed of M 8-port CSI-RS transmission resources.

As a method of selecting M 8-port CSI-RS transmission patterns fromamong five 8-port CSI-RS transmission patterns, ₅C_(M) may be used. Onlypatterns satisfying a specific condition may be pre-specified to be usedfor 8*M-port CSI-RS transmission and one pattern may be selected fromamong such patterns and indicated to the UE. Here, the specificcondition means that OFDM symbols transmitted on all antenna ports of8*M-port CSI-RSs should be transmitted only in a predetermined number ofconsecutive OFDM symbols. That is, if 16-port CSI-RSs should betransmitted in two consecutive OFDM symbols, only a method oftransmitting 16-port CSI-RSs using two of 8-port CSI-RS transmissionpatterns 1, 2 and 3 may be used. Alternatively, a method of supporting8*M-port CSI-RS transmission using only resources of consecutive indicesof the 8-port CSI-RS transmission patterns may be used. Alternatively,for 16-port CSI-RS transmission, only a method of allocating 8-portCSI-RS transmission patterns 0 and 1 and a method allocating 8-portCSI-RS transmission patterns 2 and 3 are considered and, for 16-portCSI-RS transmission, only a method of allocating 8-port CSI-RStransmission patterns 0, 1, 2 and 3 may be used.

Embodiment 3

Embodiment 3 relates to transmission of N-port CSI-RSs using only REs ofthe first region and one or more subframes. More specifically, N-portCSI-RSs are transmitted in k subframes in a state of dividing antennaports, and a CSI-RS transmission period may be a period of a subframe inwhich CSI-RSs of a single CSI-RS resource is transmitted withoutdistinction of antenna port index (that is, a periodicity (T_(CSI-RS))5, 10, 20, 40 or 80 of a subframe, in which the CSI-RS is transmitted,of Table 2). For example, if the CSI-RS transmission periodicity is Tand 64-port CSI-RSs are transmitted in two subframes in a state of beingdivided by 32 ports, CSI-RS ports 0 to 31 may be transmitted in an n-thsubframe and CSI-RS ports 32 to 64 may be transmitted in an (n+T)-thsubframe. FIG. 10(a) shows the case in which T is 5 and a subframeoffset is 3.

As another method, N-port CSI-RSs may be divisionally transmitted in Kconsecutive subframes. In this case, the subframe periodicity T_(CSI-RS)of Table 2 may be interpreted as a periodicity with which a specificCSI-RS port (e.g., CSI-RS port 0) is transmitted. In this method, if theperiodicity T_(CSI-RS) of a subframe in which the CSI-RSs aretransmitted is T and 64-port CSI-RSs are transmitted in two subframes ina state of being divided by 32 ports, CSI-RS ports 0 to 31 aretransmitted in an n-th subframe, an (n+T)-th subframe, an (n+2T)-thsubframe, . . . and CSI-RS ports 32 to 63 are transmitted in an (n+1)-thsubframe, an (n+1+T)-th subframe , an (n+1+2T)-th subframe, . . . . FIG.10(b) shows the case in which the transmission periodicity is 10subframes and a subframe offset is 3.

Preferably, RSs corresponding to ports of N-port CSI-RSs aresimultaneously transmitted for channel measurement. This is because thereceiver determines that the phase of the received signal has beenchanged if a predetermined time has elapsed although the phase of thechannel is not changed due to a difference between a transmissionfrequency generated at an oscillator of a transmitter and a frequencygenerated at an oscillator of a receiver. That is, if the transmissionfrequency is ω₀ and the frequency of the receiver is ω₀+Δ due to errors,the phase of the received signal is changed by exp(j2πΔt) with time.Therefore, if the 64-port CSI-RSs are divided by 32 ports and aretransmitted over two subframes separated by T, the phase is changed byexp(j2πΔt) between a first group including CSI-RS ports 0 to 31 and asecond group including CSI-RS ports 32 to 63. Such phase change isconsidered when determining an optimal 64-port PMI for CSI feedback.

Accordingly, if N-port CSI-RSs are divisionally transmitted in aplurality of subframes, the UE may assume that the channel is notchanged between subframes for transmitting some ports. That is, the UEmeasures the channel using the CRS in the subframe in which the CSI-RSsof two groups are transmitted, determines that change in measured valueis generated by transmission frequency errors, and performs inversecompensation therefor. More specifically, if a channel estimate measuredfrom the CRS in the subframe in which the first group including theCSI-RS ports 0 to 31 is transmitted is α₁ and a channel estimatemeasured from the CRS in the subframe in which the second groupincluding the CSI-RS ports 32 to 63 is transmitted is α₂, the UEdetermines that a phase difference of arg(α₁/α₂) is generated by adifference between transmission and reception oscillators and inverselycompensates the phase of arg(α₁/α₂) with respect to the channel estimatemeasured via the CSI-RS ports 32 to 63 transmitted in the second group.Then, an optimal PMI of 64 ports is determined along with the channelestimate measured via the CSI-RS ports 0 to 31 transmitted in the firstgroup. For inverse compensation of the phase of the UE, if one CSI-RS isdivisionally transmitted in a plurality of subframes, the CRS needs tobe necessarily transmitted in the subframes. Alternatively, if oneCSI-RS is divisionally transmitted in a plurality of subframes, thesubframes may be MBSFN subframes.

Embodiment 4

Embodiment 4 is a combination of Embodiments 1 to 3, in which the REs ofthe second region described in Embodiment 1 (including examples of FIGS.7 and 8) and the method of Embodiment 3 (including the example of FIG.9) are combined to transmit CSI-RSs.

Embodiment 5

In Embodiment 5, the second region is defined to include REs forexisting DMRS transmission. That is, positions of the 40 REs forexisting CSI-RS transmission and the positions of the 24 REs forexisting DMRS transmission are combined to transmit 64-port CSI-RSsusing all 64 REs.

Embodiment 6

In Embodiment 6, a special subframe for transmission of only CSI-RSs isdefined. In this case, the length of the PDCCH is restricted to amaximum of 2 OFDM symbols and 144 REs are used for only CSI-RStransmission at 12 OFDM symbols from a third OFDM symbol to a last OFDMsymbol. The 144 REs may be composed of a plurality of non-zero-powerCSI-RSs and a zero-power CSI-RS resources.

Apparatus Configuration of Embodiment of the Present Invention

FIG. 11 is a block diagram of a transmission point and a UE according toan embodiment of the present invention.

Referring to FIG. 11, a transmission point 1110 according to the presentinvention may include an Rx module 1111, a Tx module 1112, a processor1113, a memory 1114, and a plurality of antennas 1115. The plurality ofantennas 1115 are used to support MIMO transmission and reception. TheRx module 1111 may receive uplink signals, data and information from aUE. The Tx module 1112 may transmit downlink signals, data andinformation to a UE. The processor 1113 may provide overall control tothe operations of the transmission point 1110.

In accordance with an embodiment of the present invention, the processor1113 may process necessary information in the afore-describedmeasurement report, handover, random access, etc.

Besides, the processor 1113 processes information received by thetransmission point 1110 and information to be transmitted from thetransmission point 1110. The memory 1114 may store the processedinformation for a predetermined time and may be replaced with acomponent such as a buffer (not shown).

A UE 1120 according to the present invention may include an Rx module1121, a Tx module 1122, a processor 1123, a memory 1124, and a pluralityof antennas 1125. The plurality of antennas 1125 are used to supportMIMO transmission and reception. The Rx module 1121 may receive downlinksignals, data and information from an eNB. The Tx module 1122 maytransmit uplink signals, data and information to an eNB. The processor1123 may provide overall control to the operations of the UE 1120.

In accordance with an embodiment of the present invention, the processor1123 may process necessary information in the afore-describedmeasurement report, handover, random access, etc.

Besides, the processor 1123 processes information received by the UE1120 and information to be transmitted from the UE 1120. The memory 1124may store the processed information for a predetermined time and may bereplaced with a component such as a buffer (not shown).

One or more of the above-described embodiments of the present inventionmay apply to the configurations of the transmission point and the UE,independently or in combination. Redundant descriptions are avoided forclarity.

The description of the transmission point 1110 may apply to a relay as adownlink transmission entity or an uplink reception entity, and thedescription of the UE 1120 may apply to the relay as a downlinkreception entity or an uplink transmission entity in FIG. 11.

[Mode for Invention]

Various embodiments have been described in the best mode for carryingout the invention.

INDUSTRIAL APPLICABILITY

The embodiments of the present invention are applicable to variousmobile communication systems.

The embodiments of the present invention may be achieved by variousmeans, for example, hardware, firmware, software, or a combinationthereof. In a hardware configuration, an embodiment of the presentinvention may be achieved by one or more ASICs (application specificintegrated circuits), DSPs (digital signal processors), DSDPs (digitalsignal processing devices), PLDs (programmable logic devices), FPGAs(field programmable gate arrays), processors, controllers,microcontrollers, microprocessors, etc.

In a firmware or software configuration, an embodiment of the presentinvention may be implemented in the form of a module, a procedure, afunction, etc. Software code may be stored in a memory unit and executedby a processor. The memory unit is located at the interior or exteriorof the processor and may transmit and receive data to and from theprocessor via various known means.

The detailed description of the preferred embodiments of the presentinvention is given to enable those skilled in the art to realize andimplement the present invention. While the present invention has beendescribed referring to the preferred embodiments of the presentinvention, those skilled in the art will appreciate that manymodifications and changes can be made to the present invention withoutdeparting from the spirit and essential characteristics of the presentinvention. For example, the structures of the above-describedembodiments of the present invention can be used in combination. Theabove embodiments are therefore to be construed in all aspects asillustrative and not restrictive. Therefore, the present inventionintends not to limit the embodiments disclosed herein but to give abroadest range matching the principles and new features disclosedherein.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent invention. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of theinvention should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein. Therefore, the present invention intends not tolimit the embodiments disclosed herein but to give a broadest rangematching the principles and new features disclosed herein. It is obviousto those skilled in the art that claims that are not explicitly cited ineach other in the appended claims may be presented in combination as anembodiment of the present invention or included as a new claim by asubsequent amendment after the application is filed.

The invention claimed is:
 1. A method of transmitting channel stateinformation (CSI)-reference signals (RSs) at a base station using N (Nis a natural number) antenna ports in a wireless communication system,the method comprising: generating, by the base station, a referencesignal sequence; mapping, by the base station, the reference signalsequence to resource elements (REs) included in M patterns among fivepredefined patterns for an 8-port CSI-RS transmission, wherein M is anatural number equal to or greater than 2; and transmitting, by the basestation, the mapped reference signal, wherein N is a natural numberequal to M *
 8. 2. The method according to claim 1, wherein, if N isequal to 64, the base station further maps the reference signal sequenceto REs included in three additional patterns for the 8-port CSI-RStransmission, wherein the three additional patterns are not overlappedwith the five predefined patterns.
 3. The method according to claim 1,wherein, if N is equal to 32, the base station maps the reference signalsequence to REs included in all the five patterns.
 4. The methodaccording to claim 2, wherein: the five predefined patterns are includedin last two OFDM symbols of a first slot of a physical resource block(PRB) pair and third and fourth OFDM symbols and last two OFDM symbolsof a second slot of the PRB pair, and the three additional patterns areincluded in third and fourth OFDM symbols of the first slot of the PRBpair.
 5. The method according to claim 1, wherein the five predefinedpatterns include: a first RE, an RE having an index which is one lessthan an index of the first RE in a frequency axis direction, an REhaving an index which is one greater than an index of the first RE in atime axis direction and an RE having an index which is one less in thefrequency axis direction than an index of the RE having the index whichis one greater than an index of the first RE in the time axis direction,and a second RE, an RE having an index which is one less than an indexof the second RE in the frequency axis direction, an RE having an indexwhich is one greater than an index of the second RE in the time axisdirection and an RE having an index which is one less in the frequencyaxis direction than an index of the RE having the index which is onegreater than an index of the second RE in the time axis direction, in aphysical resource block (PRB) pair.
 6. The method according to claim 5,wherein the second RE is located to be separated from the first RE by 6subcarriers on a frequency axis.
 7. The method according to claim 6,wherein the first RE included in the first region is located at (11, 2),(9, 2), (7, 2) and (9, 5) at each slot of the PRB pair and (integer 1,integer 2)=(subcarrier index, OFDM symbol index).
 8. The methodaccording to claim 6, wherein the first RE included in the first regionis located at (11, 2), (9, 2) and (7, 2) at a first slot of the PRB pairand (integer 1, integer 2)=(subcarrier index, OFDM symbol index).
 9. Themethod according to claim 1, wherein N is one of 16, 32 or
 64. 10. Themethod according to claim 1, wherein the five predefined patternscomprise: first REs located in subcarriers #2, #3, #8 and #9 amongsubcarriers #0 to #11 on OFDM symbols #5 and #6 among OFDM symbols #0 to#13 in a physical resource block (PRB) pair, second REs located insubcarriers #4, #5, #10 and #11 among subcarriers #0 to #11 on OFDMsymbols #9 and #10 among OFDM symbols #0 to #13 in the PRB pair, thirdREs located in subcarriers #2, #3, #8 and #9 among subcarriers #0 to #11on OFDM symbols #9 and #10 among OFDM symbols #0 to #13 in the PRB pair,fourth REs located in subcarriers #0, #1, #6 and #7 among subcarriers #0to #11 on OFDM symbols #9 and #10 among OFDM symbols #0 to #13 in thePRB pair, and fifth REs located in subcarriers #2, #3, #8 and #9 amongsubcarriers #0 to #11 on OFDM symbols #12 and #13 among OFDM symbols #0to #13 in the PRB pair.
 11. A base station apparatus for transmittingchannel state information (CSI)-reference signals (RSs) using N (N is anatural number) antenna ports in a wireless communication system, thebase station apparatus comprising: a transmission module; and aprocessor, wherein the processor is configured to: generate a referencesignal sequence, map the reference signal sequence to resource elements(REs) included in M patterns among five predefined patterns for 8-portCSI-RS transmission, wherein M is a natural number equals to or greaterthan 2, and transmits the mapped reference signal, wherein N is anatural number equal to M * 8.